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Re: Alternative formulations of keywords

This page is part of the web mail archives of SRFI 89 from before July 7th, 2015. The new archives for SRFI 89 contain all messages, not just those from before July 7th, 2015.

Marc Feeley scripsit:

> If you try to formalize the cases in which it does work and the cases  
> in which it doesn't you will realize that it is very hard to specify  
> precisely.  You have to assume a particular set of powerful analyzes  
> that are performed by the compiler, and your semantics will depend on  
> the existence of these analyzes.  This places difficult constraints  
> on the Scheme implementation.

It's syntactic sugar, so I'm fine with it not working in any case that's
at all tricky.

> For example can your proposed approach work in this case:
>    (define (f g)
>      (g foo: 11 bar: 22))

Plainly no.  The compiler should cough with "keywords in call of unknown

> or in this case:
>    (define (f #!key (x 11) (y 22)) (+ x y))
>    (define (g z) (f y: z))
>    (define (h) (set! f (lambda (#!key (y 33) (z 44)) (* y z))))

Again, plainly no.  I might have said "only if the compiler can prove
that h is always called before g is", but that's precisely the sort
of tricky analysis neither of us would want to depend on.

Here the error is "keyword y: not known for function f."

In short, the definition of a function must be either global or
lexically apparent for it to be callable with keywords.

John Cowan    http://ccil.org/~cowan    cowan@ccil.org
Mr. Henry James writes fiction as if it were a painful duty.  --Oscar Wilde